The x coordinate of the rectangle, in user units. Exceptions on settingDOMException, code NO_MODIFICATION_ALLOWED_ERR Raised when the rectangle
corresponds to a read only attribute or when the object itself is
read only.

The y coordinate of the rectangle, in user units. Exceptions on settingDOMException, code NO_MODIFICATION_ALLOWED_ERR Raised when the rectangle
corresponds to a read only attribute or when the object itself is
read only.